Schizophrenia Bulletin vol. 43 no. 1 pp. 32–43, 2017
doi:10.1093/schbul/sbw132
Advance Access publication November 21, 2016
LEAD ARTICLE
Hallucinations: A Systematic Review of Points of Similarity and Difference Across
Diagnostic Classes
Flavie Waters*,1,2 and Charles Fernyhough3,4
School of Psychiatry and Clinical Neurosciences, The University of Western Australia, Perth, Western Australia, Australia; 2Clinical
Research Centre, Graylands Hospital, North Metro Health Service–Mental Health, Perth, Western Australia, Australia; 3Hearing the
Voice, c/o School of Education, Durham University, Durham, UK; 4Department of Psychology, Durham University, Durham, UK
1
*To whom correspondence should be addressed; School of Psychiatry and Clinical Neurosciences, The University of Western Australia,
35 Stirling Highway Perth, Western Australia 6009, Australia; tel: +61-8-9341-3685, fax: +61-9384-5128, e-mail: flavie.waters@health.
wa.gov.au
Hallucinations constitute one of the 5 symptom domains of
psychotic disorders in DSM-5, suggesting diagnostic significance for that group of disorders. Although specific featural
properties of hallucinations (negative voices, talking in the
third person, and location in external space) are no longer
highlighted in DSM, there is likely a residual assumption
that hallucinations in schizophrenia can be identified based
on these candidate features. We investigated whether certain
featural properties of hallucinations are specifically indicative of schizophrenia by conducting a systematic review
of studies showing direct comparisons of the featural and
clinical characteristics of (auditory and visual) hallucinations among 2 or more population groups (one of which
included schizophrenia). A total of 43 articles were reviewed,
which included hallucinations in 4 major groups (nonclinical groups, drug- and alcohol-related conditions, medical
and neurological conditions, and psychiatric disorders). The
results showed that no single hallucination feature or characteristic uniquely indicated a diagnosis of schizophrenia, with
the sole exception of an age of onset in late adolescence.
Among the 21 features of hallucinations in schizophrenia
considered here, 95% were shared with other psychiatric
disorders, 85% with medical/neurological conditions, 66%
with drugs and alcohol conditions, and 52% with the nonclinical groups. Additional differences rendered the nonclinical groups somewhat distinctive from clinical disorders.
Overall, when considering hallucinations, it is inadvisable to
give weight to the presence of any featural properties alone
in making a schizophrenia diagnosis. It is more important to
focus instead on the co-occurrence of other symptoms and
the value of hallucinations as an indicator of vulnerability.
Introduction
The personal, cultural, and clinical significances of hallucinations have changed in the 200 years since they were
defined by Esquirol as “the intimate conviction of actually perceiving a sensation for which there is no external
object.”1,2 There is a growing recognition that hallucinatory experiences attend a wide variety of psychiatric
diagnoses and can be part of everyday experience for
people who do not meet criteria for mental illness. For the
experiencer, hallucinations can have important personal
meanings, and for clinicians, they are also significant in
varied ways, including as diagnostic symptom and as factors which may impact on functioning and prognosis, and
therefore potentially the necessity of treatment.
Since the earliest clinical texts, auditory hallucinations have been closely linked to schizophrenia.3,4
Hallucinations constitute one of the 5 domains of abnormality of schizophrenia spectrum and other psychotic
disorders in DSM-5. Although not diagnostic of schizophrenia when occurring in isolation, the presence of persistent auditory hallucinations is sufficient for a diagnosis
of Other Specified Schizophrenia Spectrum and Other
Psychotic Disorder, if it is combined with clinically significant distress or functional impairment (ref.5, p. 122).
The emphasis on the clinical significance of hallucinations in DSM-55 requires closer examination given our
growing understanding of hallucinations that feature
outside of psychosis. It is increasingly recognized that
hallucinations occur with significant frequency in other
psychiatric (eg, post-traumatic stress disorder [PTSD],
personality disorders) and medical conditions (neurodegenerative conditions and eye disease) and that they are
especially predictive of multimorbid psychopathology.6,7
A predominant view, however, is that some features of
Key words: schizophrenia/bipolar disorder/psychosis/
nonclinical
© The Author 2016. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits
unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
32
Hallucinations
hallucinations may distinguish schizophrenia and related
disorders from other conditions. Candidate distinguishing features that have become important diagnostically
include negative and derogatory auditory hallucinations;
command hallucinations; voices heard conversing about
the individual in the third person; and location in external space.4,5,8
Given the status of hallucinations as diagnostic markers in DSM-5, there is a pressing need to establish their
specificity to psychotic disorders, particularly through
comparison of their featural properties across different
population groups. This exercise is also essential if we are
to understand how hallucinations function in cognitive
and neuroscientific models of psychiatric disorders such
as schizophrenia.
The present article attempts to meet this challenge
through a systematic review of empirical studies that
have made direct comparisons of hallucinations involving 2 or more population groups (one of which included
schizophrenia). Our focus is on visual and auditory hallucinations, because these experiences figure more prominently in schizophrenia research than other modalities of
hallucination. We place particular emphasis on whether
hallucinations share points of commonality or divergence between different groups. Because diagnostic criteria inevitably focus on self-report rather than objective
markers, the bulk of studies have reported on the phenomenological features of hallucinations. Too few studies
have directly compared cognitive or neuroimaging variables between 2 and more groups for meaningful analyses, although helpful syntheses of the literature exist.9–12
In this article, we present a direct contrast of hallucination features across clinical groups with a view to identifying features specific to schizophrenia. First, we briefly
consider the different conditions and groups in which
hallucinations have been reported.
Disorders and conditions in which hallucinations present
There are many disorders and conditions (including nonpathological cases) in which hallucinations have been
reported (supplementary material table 1, adapted13–15).
Psychotic experiences occur in around 4%–7% of the
general population,16,17 proving transitory in around 80%
of cases.18 In this group, incidence of hallucinations varies
with developmental stage, appearing with relatively high
prevalence in children (8%19) and older adults (community 1%–5%; residential care 63%20), and some adults on
a continuum of hallucination proneness. Hallucinations
also occur transiently in situations causing extreme physiological or psychological stress (fatigue, sensory deprivation, bereavement, etc.).21,22
Hallucinations co-occur with toxin-, alcohol-, and
drug-related conditions that affect the central nervous system and involve the cortical sensory areas. These include
intoxication with stimulants, hallucinogenic drugs, and
cannabis, and withdrawal from substances including alcohol.23 Medication-induced hallucinations also result from
drug abuse or occur as side effects of attention-deficit/
hyperactivity disorder drugs,24 antimalarial medication,25
and antiparkinsonian drugs. In these cases, hallucinations
usually disappear after withdrawal of the substance.
Hallucinations are associated with a range of medical conditions. Conditions causing interference with, or
damage to, the peripheral sensory pathways can produce hallucinations. For example, acquired deafness is
a common cause for (auditory) hallucinations, as is eye
disease or lesions of afferent visual pathways for visual
hallucinations.26,27 Endocrine-related metabolic disorders
including disorders of thyroid function28 and Hashimoto
disease29 can produce hallucinations, as can deficiencies
in D and B12 vitamins.30,31 Other medical conditions
associated with hallucinations include chromosomal disorders such as Prader–Willi syndrome,32 autoimmune disorders,33 and acquired immunodeficiency disorders such
as HIV/AIDS,34 and sleep disorders such as narcolepsy.35
Neurological events such as tumors,36,37 traumatic brain
injuries,38 epilepsy,39 and cardiovascular events may also
cause hallucinations where activity involves the brainstem
regions and areas involving the temporal, occipital, or
temporo-parietal pathways. Hallucinations are also fairly
common in neurodegenerative conditions, particularly in
Parkinson’s disease40 and dementia with Lewy bodies.41
Finally, hallucinations are reported in a range of major
psychiatric conditions. In addition to psychotic disorders
(schizophrenia, schizotypal personality traits, schizoaffective disorders, other specified spectrum disorders,
etc.), hallucinations and other psychotic experiences
occur in affective disorders such as bipolar (mixed, manic,
depressed) and unipolar depression42; personality disorders; PTSD; and anorexia and bulimia nervosa.43
In summary, because hallucinations occur in a number
of different clinical groups, they can be considered nonspecific for psychotic disorders. A categorical approach
reliant solely on the presence of hallucinations is therefore
not helpful as a diagnostic aid.
How do hallucinations present across diagnostic classes?
In this section, we consider data as they inform on points
of commonality and divergence across diagnostic classes
of psychiatric illness, with a particular focus on comparisons with schizophrenia spectrum disorders. A predominant aim is to determine which, if any, features of
hallucinations are pathognomonic: that is, specific to
schizophrenia (as the “prototypical” psychotic disorder)
and not reported in any other population group.
Methods
To answer these questions, a search was carried out in
Medline for English-language articles and book chapters containing the following terms (Hallucinat* OR
33
F. Waters & C. Fernyhough
Psychot* Symptom*) AND (Compar* OR Differen*
OR Similarit* OR Contrast*), without date restrictions. Inclusion criteria included empirical articles
involving direct contrasts between 2 and more population groups with hallucinations, where one of these
groups included schizophrenia-spectrum disorders.
Exclusion criteria were as follows: single case studies
and reviews, studies reporting on “hallucination proneness” as a continuous variable, and publication in languages other than English. The search was conducted
on June 20, 2016, and revealed 165 articles, to which 21
additional articles were added from known articles and
cross-referencing. Title and abstracts, and subsequently
the entire articles, were scanned to ascertain whether
they fulfilled the criteria (see figure 1 for PRISMA diagram). A total of 56 articles met the criteria.
The great majority of articles (90.1%) demonstrated a
focus on featural or clinical characteristics of hallucinations (supplementary material table 2). The remaining
articles reporting solely on imaging data (n = 4) or cognitive processes (n = 2) were excluded. Seven further articles
were excluded for not involving a schizophrenia group or
not reporting on hallucinations specifically.
In total, 43 articles were reviewed (see table 1). Articles
involving direct comparisons with schizophrenia included
the following 4 major groups: (1) nonclinical groups
(general population,44–48 religious experiences49,50; total 7
studies); (2) drug- or alcohol-related (substances) conditions51–59 (9 studies); (3) medical and neurological conditions (tinnitus,60 epilepsy,61,62 narcolepsy,35 other medical
and neurological causes53,63–66; total 9 studies); and (4)
psychiatric disorders (affective disorders,8,42,53,64,66–70 borderline personality disorder,71–74 PTSD,75,76 dissociative
identity disorder,44,77 anorexia78; total 18 studies). There
Records identified through
database searching
N = 165
were a further 2 articles on attenuated psychosis (ultra
high risk [UHR]),79,80 which were classed in the psychiatric group. Noticeably absent were direct comparisons
with Parkinson’s disease and other neurodegenerative
conditions. Given this important gap, we chose to include
one recent review comparing visual hallucinations in
schizophrenia to those in Parkinson’s disease, Lewy body
dementia, and eye disease81 (classed in the medical and
neurological category).
Results
Findings are organized around the 21 most commonly
described features of hallucinations in schizophrenia,
sorted according to modality, form, content, interference,
and lack of control,86 and other clinical and epidemiological features. Percentages (when available) are shown
in table 1. An entry of “nil” indicates that this feature has
not been reported in this diagnostic group.
Overall, psychiatric disorders shared the most features
with schizophrenia (20/21, 95%); followed by medical/
neurological disorders, with 18/21 features of commonality (85%); and by substance-related conditions (11/21,
66%). Nonclinical groups shared approximately half of
all features (11/21, 52%).
Auditory (verbal and other sounds) hallucinations
occurred in all 4 major groups, with the highest prevalence
(outside schizophrenia) reported in evangelical bornagain Christians (58%)50 and bipolar disorder (57%).42
The predominance of auditory hallucinations over other
modalities (eg, visual hallucinations) is commonly viewed
as indicative of schizophrenia,5 although this profile is
also reported in medical conditions including temporal
lobe epilepsy,83 as well as in bipolar disorder.42
Additional records identified from other known
articles
N = 21
Number of records screened
N = 186
Records excluded due to nonsuitability N = 130
Full-text articles assessed for
eligibility
N = 56
Full text articles excluded with
reasons:
Cognitive studies n = 2;
Neuroimaging studies n = 4;
Not involving schizophrenia =
3 (dementia, Parkinson’s
Disease, narcolepsy); Not
reporting on hallucinations = 4
Articles included in final analyses
N = 43
Fig. 1. PRISMA diagram.
34
66%
80%
50%
65%
50%
Duration: up to several hours
at a time
Perceived to be vivid and real
Originating in external space
Third-person hallucinations,
running commentary, voices
commenting
Hallucinations shared with
other people (eg, voices
“heard” by others)
60%
60%
Contents
Negative and hostile content
±58%
Nonclinical
?%
Nil
Nil
43%–53%
20%–60%
±70%
±26%
?%
±16%
Nil
±50%
Substances
20%–41%
±57%
?%
±47%
Nil
75% A, 30% V Nil
75%
Schizophrenia
Hallucinations in 3 or more
sensory modalities
Predominance of auditory (A)
over visual (V) hallucinations
Form
Presence of auditory verbal
hallucinations (“voices”)
Characteristic Features of
Hallucinations
±33%
±62%
10%–41%
±37%
±48%
±70%
±20%
±32% A,
±10% V
±32%
Medical,
Neurologic
58%–93%
±27%
40%–80%
60%–83%
54%–100%
77%–93%
±76%
±28% A,
±15% V
46%–57%
Other
Psychiatric
Nonclinical44,48 (including evangelical born-again
Christians50); cocaine withdrawal,55 alcohol dependence
disorder56; temporal lobe epilepsy62; Parkinson’s disease81;
medical and neurological condition,63 affective disorders
mixed69; PTSD,75,76 borderline personality disorder72,73;
dissociative identity disorder44,77
Epilepsy,84 neurological condition66; bipolar disorder66,69
Nonclinical28,44; cannabis abuse57; alcohol dependence
disorder53,56; medical or neurological condition,63,84
temporal lobe epilepsy62,83; affective disorders,69 dissociative
identity disorder,44 PTSD,76 borderline personality
disorder,74 narcolepsy35
Nonclinical28,44; alcohol dependence disorder51; tinnitus,60
medical or neurological condition63; dissociative identity
disorder,77 PTSD,76,77 bipolar disorder,8,64,66,69 borderline
personality disorder72–74
Nonclinical28,44,48; alcohol dependence disorder,51 cocaine
abuse55,56,59; LSD intoxication58; tinnitus,60 temporal lobe
epilepsy,62,83 medical or neurological condition63; PTSD,76
bipolar disorder,64,66,69 dissociative identity disorder,44,77
borderline personality disorder72–74
Nonclinical44 (including evangelical born-again
Christians50); alcohol dependence disorder,53 cocaine
abuse55; tinnitus,60 temporal lobe epilepsy62; dissociative
identity disorder,44 borderline personality disorder73
Cocaine abuse,55 LSD intoxication,54 alcohol dependence
disorder53; bipolar disorder,66,70 dissociative identity
disorder,77 narcolepsy35
Temporal lobe epilepsy,62,83 medical or neurological
condition63,84; bipolar disorder42,67
Nonclinical44,45,48 (including evangelical born-again
Christians50); alcohol dependence disorder,51,56 cocaine
withdrawal55; tinnitus,60 epilepsy,62,83 medical or
neurological condition,63 narcolepsy35; Parkinson’s
disease81; bipolar disorder,42,69,70 borderline personality
disorder,73,74 dissociative identity disorder,77 PTSD75
Groups Showing the Same Features as Schizophrenia
Table 1. Phenomenological Features of Hallucinations Across 4 Population Groups (%) and Comparisons With Schizophrenia (Mean %82)
Hallucinations
35
36
50%
50%
60%
30%
18–24
n/a
Trauma and neglect
External triggers
Internal triggers
Family history of psychiatric
illness
Age of onset in late teen to
early 20s
Feature commonality with
schizophrenia (number and %)
Nil
Nil
14/21 = 66%
±23%
Nil
11/21 = 52%
?%
Nil
Nil
?%
Nil
Nil
±50%
18/21 = 85%
Nil
±30%
?%
Nil
?%
Nil
Nil
?%
±53%
Nil
?%
Nil
?%
?%
±76%
±50%
Medical,
Neurologic
±89%
±30%
±4%
Nil
Nil
±42%
20%–60%
Substances
?%
50%–100%
Nonclinical
20/21 = 95%
Nil
±40%
±60%
±80%
±50%
?%
±35%
±78%
±84%
62%–82%
?%
±97%
Other
Psychiatric
Epilepsy83; cannabis abuse57; anorexia nervosa78
Nonclinical population44; tinnitus60; all substances are
internal triggers; PTSD76
Affective disorders,69 dissociative identity disorder44,77
Nonclinical population44,47; dissociative identity
disorder44,77; borderline personality disorder72,73
Tinnitus,60 medical or neurological condition,65,66
neurodegenerative disease81; UHR psychosis79
Nonclinical47,48; epilepsy62,83; PTSD,76 bipolar disorder68,85
Alcohol substance disorder51; tinnitus,60 temporal lobe
epilepsy,62,83 medical or neurological condition64,66;
borderline personality disorder,72,73 bipolar disorder66,69
Cocaine withdrawal55; tinnitus60; temporal lobe epilepsy62;
PTSD,75,76 borderline personality disorder,72,73 bipolar
disorder,64 narcolepsy35
Amphetamine withdrawal and dependence,52,55 alcohol
substance disorder56; temporal lobe epilepsy62; bipolar
disorder,69 PTSD,76 dissociative identity disorder77
Nonclinical (including evangelical born-again Christians50
and other religious voice-hearers49); cocaine withdrawal,55
LSD intoxication54; temporal lobe epilepsy62; bipolar
disorder,64 borderline personality disorder71
Nonclinical28,46 (including evangelical born-again
Christians50); cocaine withdrawal55; alcohol dependence
disorder56; medical or neurological condition63,64; temporal
lobe epilepsy62; PTSD76
Groups Showing the Same Features as Schizophrenia
Note: n/a, not applicable; LSD, lysergic acid diethylamide; UHR, ultra high risk. “Nil” findings are shaded in bold. “?%” indicates that percentages were not reported in the
articles reviewed.
?%
Hearing or vision loss
Other clinical and epidemiological features
Recurrent course of
60%
hallucinations (>1 y, multiple
episodes)
78%
Lack of perceived control
84%
Commands to commit
aggressive or injurious acts
47%
72%
Assigned significance (eg,
hallucinations have meaning)
Interference and lack of control
Interference with daytime
functions
61%
Schizophrenia
Personifications and
attributions to spiritual or
magical identities
Characteristic Features of
Hallucinations
Table 1. Continued
F. Waters & C. Fernyhough
Hallucinations
Multiple modalities of hallucinations (>3, although
not simultaneously) were originally thought to be distinctive for schizophrenia,64,66 but this pattern also occurs
in the context of drugs and alcohol,55 and narcolepsy.35
Psychiatric conditions such as bipolar disorder and dissociative identity disorder77 report several modalities of
hallucinations (typically 2 or 3), but generally fewer than
schizophrenia (where individuals may report 4 or 5 distinct modalities).
Specific formal parameters of hallucination (persistent voices, vividness and realism, and origin in external space) are also displayed in the 4 major groups. For
example, continuous voices over several hours among
those who have hallucinations have been reported in nonclinical individuals at rates of 47%,44 tinnitus (70%),60 dissociative identity disorder (93%44), and affective disorders
(77%69). Similarly, (visual) hallucinations in Parkinson’s
disease may last for hours at a time.81 The experience
is highly vivid and perceived to be real in 26% of alcohol withdrawal cases,56 bipolar disorder (100%69), and
PTSD (54%76). Voices originating in external space are
not pathognomonic of schizophrenia, occurring at rates
of 57% in nonclinical groups,44 37% in tinnitus,60 60% in
PTSD,76 83% in bipolar disorder,64,66,69 and 67% in dissociative identity disorder.44
Third-person hallucinations and voices commenting
or conversing with each other do not distinguish between
groups. Voices commenting are reported in nonclinical
groups (41% of those who hear voices)44 and in patients with
narcolepsy (17%),35 dissociative identity disorder (80%),44
and affective disorders (54%).69 Similarly third-person
hallucinations are reported at rates of 20% in nonclinical
groups,44,45 10% in narcolepsy,35 25%–60% in alcohol withdrawal,53,56 and 40% in affective disorders.69 Approximately
one-third of individuals with schizophrenia expect their
voices to be heard by others,87 a feature additionally
observed in bipolar disorder and organic psychosis.66,84
With regard to contents, negative, accusatory, or
derogatory voices occur in all groups, eg, 93% of individuals with dissociative identity disorder with hallucinations, 58% of affective disorders,69 and 62% of PTSD.76
Negative contents are also common in both auditory and
visual hallucinations in alcohol withdrawal56,88 and in neurodegenerative conditions.81 Negative voices occur less
frequently in nonclinical groups, although they are still
reported in approximately half44,48 of these individuals.
Similarly, personification and attribution of hallucinations did not distinguish between groups. Nonclinical
groups often attribute their hallucinations to a relative
or acquaintance,45 to deceased persons, and to religious
figures,46 whereas personification to supernatural entities is more common in religious experiences,50 substance-related conditions,55 and psychiatric disorders.76
In Parkinson’s disease and dementia, hallucinations are
attributed to people who may be familiar or not, alive or
deceased, or to guardian angels.81
Hallucinations assigned special significance are common in the context of drugs,54 temporal lobe epilepsy,62
bipolar disorder,64 and borderline personality disorder.71
Such special significances are also reported in religious
experiences,49,50 although the interpretation is more positive than for those in schizophrenia.
Voices giving commands to commit aggressive or injurious actions are observed in most groups. For example,
in a PTSD sample, 62% of those hearing voices were
commanded to self-harm, and 46% had acted on command hallucinations.75,76 Command hallucinations are
also reported in 82.3% of individuals with bipolar disorder.69 No data are reported on this feature in nonclinical
individuals.
Interference with daily life, and lack of perceived control, is a prominent issue in all but nonclinical groups.
For example, daytime interference is reported in 84% of
individuals with dissociative identity disorder.44 Similarly,
lack of control over the onset and content of hallucinations is common with substance-related, medical, and
neurological causes,60 as well as borderline personality
disorder72 and bipolar disorder.44 By contrast, nonclinical
groups report significantly less distress or daytime interference than individuals with schizophrenia,44 and greater
levels of control.45
A persistent course of hallucinations (lasting for more
than 1 year or multiple episodes) has been demonstrated
in nonclinical groups,47 epilepsy,83 bipolar disorder,85 and
PTSD in which hallucinations can persist for longer than
1 year in the majority of cases.76 In Leudar and coworkers’ sample of 13 nonclinical individuals,48 recurrent voice
hallucinations were reported in 89% and had been ongoing on average for longer than 4 years.
Finally, shared epidemiological and clinical features of
hallucinations include the following: (1) hearing or vision
loss as a vulnerability factor for hallucinations, which
is additionally reported in UHR groups,79 neurological
conditions including tinnitus,60 and neurodegenerative
conditions such as Parkinson’s disease81; (2) negative life
events, such as emotional neglect and trauma, reported
in nonclinical groups (50%)44 and psychiatric conditions
including dissociative identity disorder (50%)44,77 and borderline personality disorder72,73; (3) triggers that include
exogenous (external) situations in dissociative identity
disorder (at rates of 80%44) and affective disorders69 but
not nonclinical groups44, and endogenous (internal) triggers such as sadness, stress, and tiredness reported in the
nonclinical group,44 PTSD (60%),76 and tinnitus60; and (4)
family history of psychiatric illness, which is displayed
across all major groups except nonclinical groups.
One feature of hallucinations appears to distinguish
schizophrenia from other groups. Age of onset of hallucinations in schizophrenia is typically from the late teens
to early 20s. Direct comparison demonstrates that an
earlier age of onset (<12 years) is more frequent in dissociative identity disorder (33%) and nonclinical groups
37
F. Waters & C. Fernyhough
(40%) than in schizophrenia (11%).44 Daalman et al45
showed a mean age of onset of 12.4 years for nonclinical individuals compared to 21.4 years in schizophrenia.
Hallucinations in affective disorders, neurological disorders, and alcohol-related conditions, by contrast, appear
predominantly in middle or older age.56,62
Discussion of findings
Our systematic review demonstrates that almost all phenomenological, clinical, and epidemiological features of
hallucinations in schizophrenia are also represented in
other population groups, with the sole exception of age
of onset.
Points of similarity and difference among diagnostic
classes
Our findings did not support the notion that some features of hallucinations are uniquely diagnostic of schizophrenia.4,8,89 Auditory “verbal” hallucinations, which
are vivid, occur frequently, and are experienced as coming from outside of the head, are present in all 4 major
groups considered here (nonclinical, substances, medical
or neurological, and psychiatric). Examples include hallucinations linked to religious experiences,49,50 dissociative identity disorder,44,77 and temporal lobe epilepsy.62,90
Of note, voices originating in external space occurred
in half of nonclinical voice hearers,44 one-third of individuals with tinnitus,60 and 60%–83% of individuals with
PTSD,76,77 bipolar disorder,69 and dissociative identity disorder.44 The highlighting of Schneider’s first-rank symptoms (including third-person hallucinations and voices
conversing) as indicative of schizophrenia4 was not supported, with these features occurring in nonclinical samples at rates of 20%–40%,44,45 narcolepsy (10%–17%),35
alcohol withdrawal (26%–60%),53,56 affective disorders
(20%–55%),69 and dissociative identity disorder (80%).44
Similarly, the widely held notion that negative voices are
indicative of psychosis91 was not confirmed. Negative and
derogatory (visual and/or auditory) hallucinations occurred
in all (clinical and nonclinical) groups. Similarly, the way in
which hallucinations are personified and assigned special
significance (ie, seen as personally meaningful) is also a
feature of other psychiatric conditions (bipolar disorder,
borderline personality disorder, PTSD)64,71,76 and temporal
lobe epilepsy.62 In nonclinical groups (such as evangelical
born-again Christians), it is common for voices to be interpreted as having religious meaning.49,50
One feature of interest is hallucination frequency, which
is often difficult to assess empirically (e.g., ref.50) and is confounded both with symptom incidence and hallucination
duration (see table 1). Although some studies show hallucinations to be more frequent in schizophrenia in relation
to a comparison group (ref.10,80), others show hallucinations
in comparison groups to have an objectively high rate of
occurrence (e.g., refs66,69,76). In the absence of further data,
38
frequent hallucinations can thus not be considered to be
a diagnostic feature of schizophrenia. Altogether, the featural properties of hallucinations carry minimal information about the condition in which it occurs.
Only one feature, age of onset, was identified as of
potential interest for distinguishing schizophrenia from
other groups. We note, however, that this relates to a continuous variable rather than a clear presence or absence
of any hallucination feature. Its diagnostic value is further limited given the small number of studies that have
considered it transdiagnostically, the potential confound
of prodromal symptoms predating the onset of frank
psychosis, potential unreliability of reports due to difficulties in remembering a first experience that might have
occurred many years ago, and the relatively high variance
in age of onset even in schizophrenia.
With regard to points of rarity among other groups,
one feature deserving of more research concerns external
triggers for hallucination. External factors including a
lack or an excess of external stimulation (eg, social contact), are a trigger in 80% of schizophrenia cases,82 and
similar rates have been reported in dissociative identity
disorder and affective disorders.44,69 By contrast, there is
an absence of information regarding external triggers in
nonclinical groups on the basis of the one direct comparison study reviewed here.44 We note however that one
small qualitative study investigating “out-of-the-ordinary” experiences including hallucinations92 showed triggering by social isolation.
Points of rarity for major diagnostic groups
We also examined points of rarity for each major group.
A historical focus on the symptoms of psychosis has reinforced a “schizophrenia-centric” approach to hallucination
descriptions, yet our analysis allows an examination of each
disorder group individually. Specifically, table 1 enables an
inspection of how hallucination features are shared among
diagnostic groups, indicating possible points of rarity.
With regard to hallucinations in psychiatric disorders
(particularly affective disorders, borderline personality disorder, dissociative identity disorder, and PTSD),
table 1 suggests that no hallucination feature differentiated them from schizophrenia except age of onset (95%
feature commonality). This supports findings of studies
reporting on the overlap in genetic, neurobiological, and
clinical features between schizophrenia and these psychiatric disorders.93,94
Hallucinations caused by the abuse or withdrawal of
substances (toxins, drugs, alcohol) differ from schizophrenia in the following features: visual hallucinations are
more common than auditory hallucinations; the course is
not recurrent but proximally related to substance ingestion; and hearing or vision loss is not a cause.
A discussion on hallucinations in medical and neurological conditions is complicated by the heterogeneity of this
Hallucinations
group (incorporating tinnitus, epilepsy, narcolepsy, neurodegenerative conditions, and other medical and neurological conditions). Interestingly, conditions such as epilepsy
and tinnitus share up to 85% (18/21) of features with schizophrenia and appear almost indistinguishable in form and
content,60,62,84,90 except for clinical and epidemiological correlates such as trauma and external triggers. The absence of
information on triggers may merely reflect the lack of direct
comparison studies reporting on this issue. For example,
photic stimulation, TV, and video games are triggers for
complex partial seizures.95 Overall, too few direct comparisons exist for confident conclusions regarding unique hallucination features in medical and neurological conditions.
Reflecting its relative newness as a field of research
attention, only 7 studies involving nonclinical individuals
met inclusion criteria. Hallucinations in this group shared
11 out of 21 features with schizophrenia (52%), including
vivid and frequent voices, third-person hallucinations,
personification, a recurrent course of hallucinations, and
an increased risk for adverse negative events. A potential
point of rarity distinguishing this nonclinical group is
that such experiences receive a more positive interpretation compared to psychiatric disorders. Although contents may be negative96 in up to 50% of cases,44 voices are
more often positive (93% of cases compared with 83%
in schizophrenia and 67% in dissociation identity disorder) and are largely controllable. The affective reaction to
voices is also more positive in the nonclinical group. In
the sample of evangelical born-again Christians,50 voices
are actively encouraged and given positive religious meanings. Such positive interpretations are presumably consistent with reported reductions in daytime interference,
agitation, and fear, and with the fact that such individuals
do not seek care. Several studies have now described the
profile of nonclinical voice hearers as varying on a continuum with voices in schizophrenia.10,47 Additional differences identified here include that (1) other modalities
of hallucination (eg, visual or body related) may be as
common as voices (or even more so); (2) such individuals
experience a lesser total number of different modalities
of hallucinations (<3); and (3) hearing loss or visual deficits do not appear as a frequent cause.
Finally, table 1 was examined to establish whether any
hallucination features are shared among all but one diagnostic groups, suggesting a point of rarity for that exception group. This criterion was met only for the nonclinical
group. Four out of 21 (21%) hallucination features were
shared among all other groups except this one (hallucinations in ≥3 sensory modalities, commands to commit
aggressive or injurious acts, interference with daytime
functions, and lack of perceived control).
Interaction between features
The above analysis suggests that featural properties of
hallucinations alone are unlikely to be able to support a
diagnosis of schizophrenia. More important than the presence or absence of any specific hallucination features, however, is arguably the question of how those features interact
with other symptoms. Two issues need to be distinguished
here: the question of whether the specific profile of symptoms and symptom features creates distinctive signatures
for different diagnoses, and the question of how symptoms
interact as they co-occur. In relation to the first question,
table 1 indicates how a transdiagnostic comparison of hallucination features may indicate distinctive profiles for particular disorders. Clearly, in distinguishing schizophrenia
from (say) toxin-related disorders, other clinical information (such as patient history of toxin use) will be highly
relevant. Further research in transdiagnostic comparison
of symptom features (beyond their mere absence or presence) may therefore be of value in improving differential
diagnosis.
With regard to the second question, there has recently
been considerable interest in the view that psychotic symptoms occur transdiagnostically and that features of psychosis may occur on a continuum as an extended phenotype
in the general population.7 With the application of methodologies such as graph theory to psychosis research, new
methodologies are becoming available to better understand
psychosis as it operates within a network of interacting
symptoms.97 Most importantly, such methods demonstrate
how, through investigation of interactions between variables, it is possible to understand how hallucinations may
function or impact differently in different diagnostic groups
according to what roles they play in the network.
Clinical applications
This review yields an important conclusion with regard to
the diagnostic value of hallucinations. It concludes that it
is inadvisable to give weight to the presence of any featural
properties of hallucination alone when making a diagnosis. For example, negative and hostile voices talking in the
third person and causing distress may equally be present
in a patient with schizophrenia, epilepsy, brain tumor, or
PTSD. However, this conclusion does not entail that hallucinations are clinically uninformative. First, clinical
observation suggests that some conditions have their own
distinctive hallucination signature providing clues regarding their underlying causes (eg, “cocaine bugs”55). Second,
the greater clinical significance of hallucinations may lie in
their value in designating the severity of psychopathology.
The presence of hallucinations indicates increased risk of
poor outcomes transdiagnostically, including multimorbid
nonpsychotic disorders, suicidality, neurocognitive deficits, and low functioning.6,81 Functional disability is also
higher in those with hallucinations than those without
hallucinations in the context of psychiatric disorders such
as dissociative identity disorder,44 PTSD,75 anorexia nervosa,78 and narcolepsy. In such cases, hallucinations may
point to a more severe form of the disorder. Alternatively,
39
F. Waters & C. Fernyhough
hallucinations may be an experience that restricts patients’
recovery while not being intrinsic to that particular disorder, just as other factors such as educational level and
social support will influence prognosis. Altogether, the
value of hallucinations may be greater as an indicator of
vulnerability or risk than as a diagnostic marker.
Limitations and future directions
Several limitations apply to the present study. Our inclusion criteria limit the parameters and features investigated
to those that were reported in these 43 articles. The absence
of a feature in table 1 does not entail that it is a not a feature of the disorder, but rather indicates a lack of evidence
on which to make comparisons. The range of features
reviewed here is also necessarily limited. First, features
tend to cluster in similar dimensions (physical properties,
control, frequency, complexity, emotional reaction, special significance, etc.), which may exaggerate similarities
across groups of interest. Second, some features, such as
the presence of multiple personified voices96, frequency, or
the contents of visual hallucinations,81 are not represented.
Third, these features might not be the best way of describing psychopathological phenomena as natural kinds, but
may rather represent categories imposed by psychiatric
convention.98 Our analysis focused on comparison studies
involving 2 or more groups, which have generally adopted
traditional approaches to symptom assessment. Other
approaches that have used qualitative interviews and
phenomenological approaches have revealed additional
variables that do not figure in the above contrasts. It is
possible that studies targeting variables such as changed
aspects of self-consciousness, disturbed sense of internal
space,99 bodily sensations,96 and thought-like properties of
voices,96 may reveal hallucination features that are more
discriminative of psychosis than those considered here.
Furthermore, the present analysis might have had a different outcome if we had seeded our comparisons with
a diagnostic group other than schizophrenia, such as
Parkinson’s disease, where the features for comparison
might have been significantly different. We could have also
have adopted different criteria, such as comparison of hallucinations among 2 or more diagnostic groups without
the requirement that one be schizophrenia. A final limitation is that the studies reviewed adopted widely varying
measures and designs. Further progress in transdiagnostic
comparison of hallucination features arguably requires
consistency of measures across the groups studied.100
Finally, we consider implications for cognitive and neuroscientific models of hallucinations. We noted at the outset that there is very limited evidence in the cognitive and
neuroscientific domains on which to base transdiagnostic
comparisons of hallucinations. A further issue concerns the
problem of mapping cognitive profiles of different groups
to specific features of hallucinations, as opposed to their
mere presence or absence. Mostly such research compares
40
diagnostic groups with healthy controls or (increasingly)
uses hallucination incidence as an independent variable
within a particular diagnostic group: eg, comparing schizophrenia patients with and without hallucinations.
For these and other reasons, a discussion and comparison of cognitive and neurobiological models across diagnostic groups is beyond the scope of the present article.
There are well-developed models of hallucinations in
schizophrenia9,11,101,102 and in neurodegenerative disease
such as Parkinson’s disease.103–105 A complication is that
the models for these disorder groups are rather divergent,
with some schizophrenia models proposing hyperactivity of the auditory cortex mediated by dopamine release
and Parkinson’s models proposing underactivity of the
occipital cortex mediated by acetylcholine. No such
models have been developed for other conditions except
for nonclinical hallucinations, which some continuum
approaches propose can be best understood as variants
of schizophrenia models. Given the many featural similarities of hallucinations among the disorders discussed
here, further effort is needed in developing and integrating neurocognitive models across diagnostic groups.
Conclusions
Hallucinations are a feature of human experience that
crosses diagnostic category boundaries and straddles the
divide between psychopathological and nonclinical experience. They occur widely across diagnostic disorders and
their presence or absence is only clinically useful when
considered in conjunction with other symptoms and clinically relevant data. There are no “points of rarity” when
we address the features of hallucinations in schizophrenia,
with the possible exception of age of onset. We recommend that future studies systematically ask about onset,
and the conditions and context in which hallucination first
occurred.106,107 Other features may be particularly valuable in distinguishing other disorders, but more research
is needed which pays attention to phenomenological and
clinical features of hallucinations and compares them in
methodologically robust designs across diagnostic groups
and into the nonclinical population.
Supplementary Material
Supplementary material is available at http://schizophreniabulletin.oxfordjournals.org.
Funding
Wellcome Trust (WT108720 to C.F.).
Acknowledgment
The authors have declared that there are no conflicts of
interest in relation to the subject of this study.
Hallucinations
References
1.Esquirol E. Mental Maladies; A Treatise on Insanity.
Philadelphia, PA: Lea and Blanchard; 1845.
2.Berrios GE. The History of Mental Symptoms: Descriptive
Psychopathology Since the Nineteenth Century. Cambridge,
UK: Cambridge University Press; 1996.
3. Diefendorf AR, Kraepelin E. Clinical Psychiatry: A Textbook
for Students and Physicians. Abstracted and adapted from the
7th German edition of Kraepelin’s Lehrbuch der Psychiatrie,
new ed., rev. and augment. New York, NY: MacMillan; 1907.
4. Schneider K. Clinical Psychopathology, trans. by Hamilton
MW. New York, NY: Grune & Stratton; 1959.
5. American Psychiatric Association. Diagnostic and Statistical
Manual of Mental Disorders. 5th ed. Washington, DC:
American Psychiatric Association; 2013.
6.Kelleher I, Devlin N, Wigman JT, et al. Psychotic experiences in a mental health clinic sample: implications for suicidality, multimorbidity and functioning. Psychol Med.
2014;44:1615–1624.
7.van Os J, Reininghaus U. Psychosis as a transdiagnostic
and extended phenotype in the general population. World
Psychiatry. 2016;15:118–124.
8.Junginger J, Frame CL. Self-report of the frequency and
phenomenology of verbal hallucinations. J Nerv Mental Dis.
1985;173:149–155.
9. Waters F, Allen P, Aleman A, et al. Auditory hallucinations
in schizophrenia and nonschizophrenia populations: a review
and integrated model of cognitive mechanisms. Schizophr
Bull. 2012;38:683–693.
10.Johns LC, Kompus K, Connell M, et al. Auditory verbal
hallucinations in persons with and without a need for care.
Schizophr Bull. 2014;40(suppl 4):S255–S264.
11. Alderson-Day B, Diederen K, Fernyhough C, et al. Auditory
hallucinations and the Brain’s resting-state networks: findings and methodological observations. Schizophr Bull. 2016.
doi:10.1093/schbul/sbw078.
12.de Leede-Smith S, Barkus E. A comprehensive review of
auditory verbal hallucinations: lifetime prevalence, correlates
and mechanisms in healthy and clinical individuals. Front
Hum Neurosci. 2013;7:367.
13.
Brasic JR. Hallucinations. Percept Motor Skills.
1998;86:851–877.
14. Keshavan MS, Kaneko Y. Secondary psychoses: an update.
World Psychiatry. 2013;12:4–15.
15.Stephane M, Starkstein S, Pahissa J. Psychosis in general
medical and neurological conditions. In: Waters F, Stephane
M, eds. The Assessment of Psychosis: A Reference Book and
Rating Scales for Research and Practice. Chap. 13. 1st ed.
New York, NY: Routledge; 2014:136–149.
16. Eaton W, Romanoski A, Anthony JC, Nestadt G. Screening
for psychosis in the general population with a self-report
interview. J Nerv Mental Dis. 1991;179:689–693.
17. Tien AY. Distributions of hallucinations in the population.
Soc Psychiatry Psychiatr Epidemiol. 1991;26:287–292.
18. Linscott R, Van Os J. An updated and conservative systematic review and meta-analysis of epidemiological evidence
on psychotic experiences in children and adults: on the pathway from proneness to persistence to dimensional expression
across mental disorders. Psychol Med. 2013;43:1133–1149.
19. McGee R, Williams S, Poulton R. Hallucinations in nonpsychotic children. J Am Acad Child Adolesc Psychiatry.
2000;39:12–13.
20. Zayas EM, Grossberg GT. The treatment of psychosis in late
life. J Clin Psychiatry. 1998;59(suppl 1):5–10.
21. Bexton WH, Heron W, Scott TH. Effects of decreased variation in the sensory environment. Can J Psychol. 1954;8:70.
22. Mason OJ, Brady F. The psychotomimetic effects of short-term
sensory deprivation. J Nerv Mental Dis. 2009;197:783–785.
23. Smith MJ, Thirthalli J, Abdallah AB, Murray RM, Cottler LB.
Prevalence of psychotic symptoms in substance users: a comparison across substances. Compr Psychiatry. 2009;50:245–250.
24.Mosholder AD, Gelperin K, Hammad TA, Phelan K,
Johann-Liang R. Hallucinations and other psychotic symptoms associated with the use of attention-deficit/hyperactivity
disorder drugs in children. Pediatrics. 2009;123:611–616.
25.Lebain P, Juliard C, Davy J, Dollfus S. Neuropsychiatric
symptoms in preventive antimalarial treatment with mefloquine: apropos of 2 cases. L’Encephale. 1999;26:67–70.
26. Hammeke TA, McQuillen MP, Cohen BA. Musical hallucinations associated with acquired deafness. J Neurol Neurosurg
Psychiatry. 1983;46:570–572.
27. ffytche DH. Visual hallucinations in eye disease. Curr Opin
Neurol. 2009;22:28–35.
28. Davis AT. Psychotic states associated with disorders of thyroid function. Int J Psychiatry Med. 1990;19:47–56.
29. Alink J, de Vries TW. Unexplained seizures, confusion or hallucinations: think Hashimoto encephalopathy. Acta Paediatr.
2008;97:451–453.
30. Raveendranathan D, Shiva L, Venkatasubramanian G, Rao MG,
Varambally S, Gangadhar BN. Vitamin B12 deficiency masquerading as clozapine-resistant psychotic symptoms in schizophrenia. J Neuropsychiatry Clin Neurosci. 2013;25:E34–E35.
31. Stumpf WE, Privette TH. Light, vitamin D and psychiatry.
Psychopharmacology. 1989;97:285–294.
32.Vogels A, Hert MD, Descheemaeker M, et al. Psychotic
disorders in Prader–Willi syndrome. Am J Med Genet A.
2004;127:238–243.
33.Kayser MS, Dalmau J. The emerging link between autoimmune disorders and neuropsychiatric disease. J
Neuropsychiatry Clin Neurosci. 2011;23:90–97.
34. De Ronchi D, Bellini F, Cremante G, et al. Psychopathology
of first-episode psychosis in HIV-positive persons in comparison to first-episode schizophrenia: a neglected issue. AIDS
Care. 2006;18:872–878.
35. Fortuyn HAD, Lappenschaar G, Nienhuis FJ, et al. Psychotic
symptoms in narcolepsy: phenomenology and a comparison
with schizophrenia. Gen Hosp Psychiatry. 2009;31:146–154.
36. Teeple RC, Caplan JP, Stern TA. Visual hallucinations: differential diagnosis and treatment. Prim Care Companion J Clin
Psychiatry. 2009;11:26–32.
37.Madhusoodanan S, Danan D, Brenner R, Bogunovic O.
Brain tumor and psychiatric manifestations: a case report
and brief review. Ann Clin Psychiatry. 2004;16:111–113.
38. Sachdev P, Smith J, Cathcart S. Schizophrenia-like psychosis
following traumatic brain injury: a chart-based descriptive
and case–control study. Psychol Med. 2001;31:231–239.
39.Trimble M, Kanner A, Schmitz B. Postictal psychosis.
Epilepsy Behav. 2010;19:159–161.
40. Fenelon G. Hallucinations in Parkinson’s disease. In: Laroi
F, Aleman A, eds. Hallucinations: A Guide to Treatment
and Management. Chap. 19. 1st ed. Oxford, UK: Oxford
University Press; 2010:351–376.
41. Sanchez-Castaneda C, Rene R, Ramirez-Ruiz B, et al. Frontal
and associative visual areas related to visual hallucinations
41
F. Waters & C. Fernyhough
in dementia with Lewy bodies and Parkinson’s disease with
dementia. Mov Disord. 2010;25:615–622.
42.Baethge C, Baldessarini R, Freudenthal K, Streeruwitz A.
Hallucinations in bipolar disorder: characteristics and comparison to unipolar depression and schizophrenia. Bipolar
Disord. 2005;7:136–145.
43.Miotto P, Pollini B, Restaneo A, et al. Symptoms of psychosis in anorexia and bulimia nervosa. Psychiatry Res.
2010;175:237–243.
44. Honig A, Romme MAJ, Ensink BJ, Escher SD, Pennings MHA,
Devries MW. Auditory hallucinations: a comparison between
patients and nonpatients. J Nerv Ment Dis. 1998;186:646–651.
45. Daalman K, Boks MP, Diederen KM, et al. The same or different? A phenomenological comparison of auditory verbal
hallucinations in healthy and psychotic individuals. J Clin
Psychiatry. 2011;72:320–325.
46.Lindal E, Stefansson G, Stefansson S. The qualitative difference of visions and visual hallucinations: a comparison
of a general-population sample and clinical sample. Compr
Psychiatry. 1994;35:405–408.
47.Peters E, Ward T, Jackson M, et al. Clinical, socio-demographic and psychological characteristics in individuals with
persistent psychotic experiences with and without a “need for
care”. World Psychiatry. 2016;15:41–52.
48. Leudar I, Thomas P, McNally D, Glinski A. What voices can
do with words: pragmatics of verbal hallucinations. Psychol
Med. 1997;27:885–898.
49.Cottam S, Paul S, Doughty O, Carpenter L, Al-Mousawi
A, Karvounis S, Done D. Does religious belief enable positive interpretation of auditory hallucinations? A comparison
of religious voice hearers with and without psychosis. Cogn
Neuropsychiatry. 2011;16:403–421.
50. Davies MF, Griffin M, Vice S. Affective reactions to auditory
hallucinations in psychotic, evangelical and control groups.
Br J Clin Psychol. 2001;40:361–370.
51. Alpert M, Silvers KN. Perceptual characteristics distinguishing auditory hallucinations in schizophrenia and acute alcoholic psychoses. Am J Psychiatry. 1970;127:298–393.
52. Bell D. Comparison of amphetamine psychosis and schizophrenia. Br J Psychiatry. 1965;111:701–707.
53. Goodwin D, Alderson P, Rosenthal R. Clinical significance
of hallucinations in psychiatric disorders: a study of 116 hallucinatory patients. Arch Gen Psychiatry. 1971;24:76–78.
54.Malitz S, Wilkens B, Esecover H. A comparison of druginduced hallucinations with those seen in spontaneously
occurring psychosis. In: West LJ, ed. Hallucinations. Chap 5.
1st ed. New York, NY: Grune & Stratton; 1962:50–63.
55.Mitchell J, Vierkant AD. Delusions and hallucinations of
cocaine abusers and paranoid schizophrenics: a comparative
study. J Psychol. 1991;125:301–310.
56. Mott RH, Iver FS, Anderson JM. Comparative study of hallucinations. Arch Gen Psychiatry. 1965;12:595–601.
57.Núñez L, Gurpegui M. Cannabis-induced psychosis: a
cross-sectional comparison with acute schizophrenia. J Clin
Psychiatry. 2002;63:812–816.
58.Young BG. A phenomenological comparison of LSD and
schizophrenic states. Br J Psychiatry. 1974;124:64–74.
59.Aggernaes A. The experienced reality of hallucinations
and other psychological phenomena. Acta Psychiatr Scand.
1972;48:220–238.
60. Johns LC, Hemsley D, Kuipers E. A comparison of auditory
hallucinations in a psychiatric and nonpsychiatric group. Br J
Clin Psychol. 2002;41:81–86.
42
61.Perez M, Trimble M, Murray N, Reider I. Epileptic psychosis: an evaluation of PSE profiles. Br J Psychiatry.
1985;146:155–163.
62. Slater E, Beard A. The schizophrenia-like psychoses of epilepsy. Br J Psychiatry. 1963;109:95–112.
63.Cutting J. The phenomenology of acute organic psychosis. Comparison with acute schizophrenia. Br J Psychiatry.
1987;151:324–332.
64. Frieske DA, Wilson WP. Formal qualities of hallucinations:
a comparative study of the visual hallucinations in patients
with schizophrenic, organic, and affective psychoses. Proc
Annu Meet Am Psychopathol Assoc. 1966;54:49–62.
65.Johnstone EC, Cooling N, Frith CD, Crow T, Owens D.
Phenomenology of organic and functional psychoses and the
overlap between them. Br J Psychiatry. 1988;153:770–776.
66. Lowe GR. The phenomenology of hallucinations as an aid to
differential diagnosis. Br J Psychiatry. 1973;123:621–633.
67.Bowman K, Raymond A. A statistical study of hallucinations in the manic-depressive psychoses. Am J Psychiatry.
1931;88:299–309.
68. Chaturvedi SK, Sinha VK. Recurrence of hallucinations in
consecutive episodes of schizophrenia and affective disorder.
Schizophr Res. 1990;3:103–106.
69.Okulate GT, Jones OB. Auditory hallucinations in schizophrenic and affective disorder Nigerian patients: phenomenological comparison. Transcult Psychiatry. 2003;40:531–541.
70. Shinn AK, Pfaff D, Young S, Lewandowski KE, Cohen BM,
Öngür D. Auditory hallucinations in a cross-diagnostic sample of psychotic disorder patients: a descriptive, cross-sectional study. Compr Psychiatry. 2012;53:718–726.
71.Hepworth CR, Ashcroft K, Kingdon D. Auditory hallucinations: a comparison of beliefs about voices in individuals
with schizophrenia and borderline personality disorder. Clin
Psychol Psychother. 2013;20:239–245.
72. Kingdon DG, Ashcroft K, Bhandari B, et al. Schizophrenia
and borderline personality disorder: similarities and differences in the experience of auditory hallucinations, paranoia,
and childhood trauma. J Nerv Ment Dis. 2010;198:399–403.
73.Slotema CW, Daalman K, Blom JD, Diederen KM, Hoek
HW, Sommer IE. Auditory verbal hallucinations in patients
with borderline personality disorder are similar to those in
schizophrenia. Psychol Med. 2012;42:1873–1878.
74. Tschoeke S, Steinert T, Flammer E, Uhlmann C. Similarities and
differences in borderline personality disorder and schizophrenia with voice hearing. J Nerv Mental Dis. 2014;202:544–549.
75. Hamner MB, Frueh BC, Ulmer HG, et al. Psychotic features
in chronic posttraumatic stress disorder and schizophrenia:
comparative severity. J Nerv Mental Dis. 2000;188:217–221.
76. Jessop M, Scott J, Nurcombe B. Hallucinations in adolescent
inpatients with post-traumatic stress disorder and schizophrenia: similarities and differences. Australas Psychiatry.
2008;16:268–272.
77. Dorahy MJ, Shannon C, Seagar L, et al. Auditory hallucinations in dissociative identity disorder and schizophrenia with
and without a childhood trauma history: similarities and differences. J Nerv Mental Dis. 2009;3:892–898.
78.Eagles JM, Wilson AM, Hunter D, Callender JS. A comparison of anorexia nervosa and affective psychosis in young
females. Psychol Med. 1990;20:119–123.
79. Kimhy D, Corcoran C, Harkavy-Friedman JM, et al. Visual
form perception: a comparison of individuals at high risk
for psychosis, recent onset schizophrenia and chronic schizophrenia. Schizophr Res. 2007;97:25–34.
Hallucinations
80. Brett C, Peters E, McGuire P. Which psychotic experiences
are associated with a need for clinical care? Eur Psychiatry.
2015;30:648–654.
81. Waters F, Collerton D, Blom JD, et al. Visual hallucinations
in the psychosis-spectrum, and comparative information
from neurodegenerative disorders and eye disease. Schizophr
Bull. 2014;40(suppl 4):S233–S245.
82.Nayani TH, David AS. The auditory hallucination: a phenomenological survey. Psychol Med. 1996;26:177–189.
83. Toone BK, Garralda ME, Ron MA. The psychoses of epilepsy and the functional psychoses: a clinical and phenomenological comparison. Br J Psychiatry. 1982;141:256–261.
84. Standage K. Schizophreniform psychosis among epileptics in
a mental hospital. Br J Psychiatry. 1973;123:231–232.
85.Dell’Osso L, Akiskal HS, Freer P, Barberi M, Placidi GF,
Cassano GB. Psychotic and nonpsychotic bipolar mixed
states: comparisons with manic and schizoaffective disorders.
Eur Arch Psychiatry Clin Neurosci. 1993;243:75–81.
86. Larøi F, Sommer IE, Blom JD, et al. The characteristic features of auditory verbal hallucinations in clinical and nonclinical groups: state-of-the-art overview and future directions.
Schizophr Bull. 2012;38:724–733.
87. Oulis PG, Mavreas VG, Mamounas JM, Stefanis CN. Clinical
characteristics of auditory hallucinations. Acta Psychiatr
Scand. 1995;92:97–102.
88.Bliss EL, Clark LD. Visual hallucinations. In: West LJ, ed.
Hallucinations. New York, NY: Grune & Stratton; 1962:92–108.
89. American Psychiatric Association. Diagnostic and Statistical
Manual of Mental Disorders. 4th ed., revised. Washington,
DC: American Psychiatric Association; 2000.
90.Perez M, Trimble MR. Epileptic psychosis—diagnostic
comparison with process schizophrenia. Br J Psychiatry.
1980;137:245–249.
91. Close H, Garety P. Cognitive assessment of voices: further
developments in understanding the emotional impact of
voices. Br J Clin Psychol. 1998;37:173–188.
92. Heriot-Maitland C, Knight M, Peters E. A qualitative comparison of psychotic-like phenomena in clinical and non-clinical populations. Br J Clin Psychol. 2012;51:37–53.
93. Lichtenstein P, Yip BH, Björk C, et al. Common genetic determinants of schizophrenia and bipolar disorder in Swedish
families: a population-based study. Lancet. 2009;373:234–239.
94. Buckley PF, Miller BJ, Lehrer DS, Castle DJ. Psychiatric comorbidities and schizophrenia. Schizophr Bull. 2009;35:383–402.
95. Motooka H, Ueki H, Ishida S, Maeda H. Ictal visual hallucination intermittent photic stimulation: using evaluation of
the clinical findings, ictal EEG, ictal SPECT, and rCBF. No to
Shinkei. 1999;51:791–797.
96. Woods A, Jones N, Alderson-Day B, Callard F, Fernyhough
C. Experiences of hearing voices: analysis of a novel phenomenological survey. Lancet Psychiatry. 2015;2:323–331.
97. Wigman JT, de Vos S, Wichers M, van Os J, Bartels-Velthuis
AA. A transdiagnostic network approach to psychosis.
Schizophr Bull. 2017;43:122–123.
98.Kendell RE. The Role of Diagnosis in Psychiatry. Oxford,
UK: Blackwell Scientific Publications; 1975.
99.Henriksen MG, Raballo A, Parnas J. The pathogenesis of
auditory verbal hallucinations in schizophrenia: a clinical–phenomenological account. Philos Psychiatry Psychol.
2015;22:165–181.
100. Kelleher I. Auditory hallucinations in the population: what
do they mean and what should we do about them? Acta
Psychiatr Scand. 2016;134:3–5.
101. Allen P, Modinos G, Hubl D, et al. Neuroimaging auditory
hallucinations in schizophrenia: from neuroanatomy to neurochemistry and beyond. Schizophr Bull. 2012;38:695–703.
102.Garety PA, Bebbington P, Fowler D, Freeman D, Kuipers
E. Implications for neurobiological research of cognitive models of psychosis: a theoretical paper. Psychol Med.
2007;37:1377–1391.
103. Collerton D, Perry E, McKeith I. Why people see things that
are not there: a novel Perception and Attention Deficit model
for recurrent complex visual hallucinations. Behav Brain Sci.
2005;28:737–757; discussion 757–794.
104.Diederich NJ, Fénelon G, Stebbins G, Goetz CG.
Hallucinations in Parkinson disease. Nat Rev Neurol.
2009;5:331–342.
105. Howard R, Brammer M, David A, Woodruff P, Williams S.
The anatomy of conscious vision: an fMRI study of visual
hallucinations. Nat Neurosci. 1998;1:738–742.
106. Carter DM, Mackinnon A, Howard S, Zeegers T, Copolov
DL. The development and reliability of the Mental Health
Research Institute Unusual Perceptions Schedule (MUPS):
an instrument to record auditory hallucinatory experience.
Schizophr Res. 1995;16:157–165.
107. Escher S, Hage P, Romme M, Romme M. Maastricht Interview
With a Voice Hearer. Understanding Voices: Coping With
Auditory Hallucinations and Confusing Realities. Gloucester,
UK: Handsell; 2000.
43